Ultrasonic flow meters have many advantages over other methods of determining flow rates. Ultrasonic flow meters can continuously measure the flow rate, while other methods generally measure average flow rates. In addition, ultrasonic flow meters are obstructionless and work with non-conductive fluids.
Ultrasonic flow meters have a pair of transducers that are placed on either side of the flow path of a fluid flowing through a conduit. The transducers are pointed at each other and placed on either side of the flow path of a fluid flowing through a pipe. The line between the transducers has a component in the direction of the fluid flow. The principle used to detect flow rates is that the transit time of an ultrasonic packet will increase in the upstream and decrease in the downstream path. The amount by which the transit time changes is directly proportional to the flow rate. It is well known that ultrasonic flow meters have fixed offsets. Normally the offset is measured by having the ultrasonic flow meter measure the flow rate with no fluid flow through the meter. The meter should read zero so any reading is an offset that is subtracted from all future readings. This process is performed manually by adjusting a potentiometer. Unfortunately, the offset can drift over time, especially in the case of clamp-on transducers. In addition, this technique only compensates for static (no-flow) offsets and does not take into account offset that occur when a fluid is flowing through the meter.
Thus there exists a need for a calibration method that can automatically detect both static and dynamic offsets in an ultrasonic flow meter and compensate for both offsets.